1. Technical Field
The present invention relates generally to systems for controlling the hydraulic line pressure in an electronic automatic transmission and, more particularly, to a pressure regulator having a solenoid-actuated valve for adaptively controlling the level of hydraulic line pressure delivered to frictional elements within the transmission based on the difference between transducer sensed line pressure and desired line pressure.
2. Discussion
Generally speaking, land vehicles require three basic components: a power plant such as an internal combustion engine, a powertrain and wheels. The function of the powertrain is to transmit torque generated by the power plant to the wheels thereby providing movement of the vehicle. A powertrain's main component is typically referred to as the transmission. Engine torque and speed are converted in the transmission in accordance with the tractive power demand of the vehicle to propel the vehicle. The vehicle's transmission is also capable of controlling the direction of rotation being applied to the wheels so that the vehicle may be driven both forward and backward.
An automatic transmission typically includes a hydrodynamic torque converter to smoothly transfer engine torque from the engine crankshaft to the transmission input shaft through fluid flow forces. The transmission also includes frictional elements or clutch assemblies which couple the transmission input shaft through one or more planetary gear sets to provide various ratios of torque to the transmission output shaft. The output shaft is usually connected to the drive wheels via a differential.
A hydraulic control assembly engages and disengages the frictional elements which transfer torque through the transmission and effect gear changes in the transmission. Various components, such as spring-biased spool valves, spring-biased accumulators and ball check valves, direct and regulate the fluid flow in the hydraulic control assembly. A hydraulic pump provides fluid pressure and flow rate to energize the hydraulic components in the assembly. Sufficient hydraulic line pressure is required to engage the frictional elements and prevent slippage therebetween to transmit torque from the transmission input shaft to the transmission output shaft. If insufficient line pressure is provided, the frictional elements do not fully engage and slip occurs resulting in power loss and damage to the transmission. Conversely, if excessive line pressure is provided, the hydraulic pump torque is higher than necessary resulting in decreased fuel efficiency of the vehicle.
On level ground, constant throttle and low-load conditions, high line pressure is not required to prevent the clutches from slipping. Since the line pressure is produced by utilizing energy from the engine, a lower pressure demand consumes less energy from the engine. Therefore, controlling the operating parameters to adjust the pressure requirements based on transmission needs reduces parasitic losses and improves powertrain efficiency.
It is well known that a fixed displacement pump and a pressure regulator may be used to maintain the appropriate line pressure. These systems rely on springs to provide a predetermined fluid flow rate and pressure for various operating conditions. Thus, once the transmission is designed, the operating condition of the hydraulic system is fixed. It is also well known to use a variable displacement pump in place of the fixed displacement pump and pressure regulator. These pumps are considerably more costly than fixed displacement pumps.
A thorough description of general automatic transmission design principles may be found in "Fundamentals of Automatic Transmissions and Transaxles", Chrysler Corporation Training Manual No. TM-508A. Additional descriptions of automatic transmissions may be found in co-assigned U.S. Pat. No. 3,631,744, entitled "Hydrodynamic Transmission", issued on Jan. 4, 1972 to Blomquist, et al., and U.S. Pat. No. 4,289,048, entitled "Lock Up system for Torque Converter", issued on Sep. 15, 1981 to Mikel, et al. These patents are hereby incorporated by reference.
In recent years, a more advanced form of transmission control system has been proposed, which offers the possibility of enabling the transmission to learn and adapt itself to changing conditions. In this regard, co-assigned U.S. Pat. No. 3,956,947, issued on May 18, 1976 to Leising, et al. and U.S. Pat. No. 5,458,545, issued Oct. 17, 1995 to Adam et al., set forth a fundamental development in this field and are hereby incorporated by reference. Specifically, these patents disclose automatic transmission designs which feature an adaptive control system that includes electronically operated solenoid-actuated valves for providing closed-loop control of various functions in the hydraulic control assembly.
3. Objects of the Present Invention
In view of the foregoing, it is one of the principal objects of the present invention to provide a system for continually controlling the hydraulic line pressure in an automatic transmission such that the minimum line pressure necessary for full engagement of the frictional elements based on the characteristics and current operating condition of the automatic transmission is provided thereby improving transmission efficiency and increasing the fuel economy of the vehicle.
It is another object of the present invention to provide a control system for controlling hydraulic line pressure based on transducer sensed line pressure input to a transmission controller.
It is yet another object of the present invention to provide an adaptive system for controlling the hydraulic line pressure having a fast response time, allowing the control strategy to operate at minimum line pressure levels, yet increasing line pressure quickly when necessary.
It is another object of the present invention to learn the minimum pressure required by actually lowering the pressure until slip is observed (measured). The amount of slip, however, is so small that no disturbance is noticed by the driver.
It is still yet another object of the present invention to provide a method for controlling the hydraulic line pressure in an automatic transmission such that a minimum required line pressure is provided to frictional elements to prevent them from slipping thereby improving transmission efficiency and increasing the fuel economy of the vehicle.
It is a further object of the present invention to provide a method for adaptively controlling the hydraulic line pressure, such that corrections to the methodology are incorporated based on prior operational conditions of the transmission operation.
It is yet another object of the invention is to provide a control system where the control actuation can be continuously corrected as a function of target pressure and operating pressure.